Bush has been in intensive care since Sunday, McGrath said in a statement later today.

Here's McGrath's full statement:

“Following a series of setbacks including a persistent fever, President Bush was admitted to the intensive care unit at Methodist Hospital on Sunday where he remains in guarded condition. Doctors at Methodist continue to be cautiously optimistic about the current course of treatment. The President is alert and conversing with medical staff, and is surrounded by family.”

Bush has remained hospitalized for most of the last two months. He was first admitted from Nov. 7-19, and then he was re-admitted to Houston's Methodist Hospital on Nov. 23. CNN noted that Bush spent Christmas with his family and that he is in good spirits, but that doctors have still not produced a cause for the fever.

"The president has made very slight improvement, but still no discussion of discharge and doctors remain cautiously optimistic," McGrath told CNN.

Bush was initially admitted for bronchitis and a lingering cough. McGrath told the AP that it has improved. Now, doctors are dealing only with the "stubborn fever."

"It's an elevated fever, so it's actually gone up in the last day or two," McGrath told the AP. "It's a stubborn fever that won't go away."